Hello, does anyone know the startup air compressor requirements. I know the unit requires 100 PSI, but I don't know the CFM.

Thanks,

 

@da_souljah,

Are you referring to the compressed air requirements during the start-up process of the machine?

Or does the machine you are working on have an air compressor described as the Startup Air Compressor?

Are you trying to use an AC motor-driven air compressor to replace the extraction air used to supply the compressor bleed valves and solenoid-operated air valves?

How old is the machine you are working on?

I have seen some "small" air compressors used for GE-design heavy duty gas turbines with 10- or 15-gallon tanks that worked pretty well. If you look at the P&IDs for the machine you will see that most air-operated devices don't normally require a lot of flow--with the exception of the compressor bleed valves which need a lot of flow when being closed during starting. And, a tank of a minimum of 15 gallons should handle that reasonably well (the logic for the compressor bleed valves to be closed after being commanded to close is usually 11 seconds so the valves don't have to be closed quickly--but they do have to close).

The thing you want to take into consideration if you're trying to eliminate the extraction air of the machine is that the compressed air supply should be clean and dry. Many of the smaller solenoid-operated pneumatic devices on the machine have pressure regulators--with moisture capture glass "bottles"--to prevent moisture from getting into the actuators. The compressor bleed valves don't have pressure regulators or moisture "traps" and they DO need clean, dry instrument air. Draining moisture from the the tank of an air compressor regularly that's being used for compressed air supply for a GE-design heavy duty gas turbine should be a priority.

GE doesn't normally provide the compressed air volumetric flow-rate requirements of their machines, though some research using the nameplates of the devices could yield a reasonably good estimate.

If you have something else in mind, please clarify your request.

 

Thanks for the response. The machines do indeed each have an air compressor described as the "Startup Air Compressor". The machines were put into service around 1999. The original air compressors were reciprocating 7.5HP, that provided 125 psi at about 30-40cfm. The new compressors installed about 2 years ago are Ingersol Rand rotary screw compressors, that have been nothing but a headache. I want to get those rotary screws eventually changed out, but I couldn't find anywhere in the 7EA manuals/literature the startup air demands.

 

@da_souljah,

Hmmmm. I can't imagine what a (single) Startup Air Compressor would be required for--especially if it's only running during start-up. I presume you are going to say that there are valves to be able to use one or more of the other air compressors during startup if one machine's compressor fails or is unavailable.?.?.?

Do these machines have some unusual need for compressed air during startup. And by startup I am referring to initial cranking/purging, firing, warm-up, and acceleration to FSNL and synchronization. Or do these compressors run during loaded operation, as well? In which case it would be unusual to have a single air compressor as it could be a single point of failure that prevents operation. Again, I'm struggling to understand why a Startup Air Compressor is required for a typical GE-design heavy duty gas turbine. I'm not saying there has never been machines with Startup Air Compressors--but in forty years of working on GE-design heavy duty gas turbines I've never seen a machine equipped with a (single) Start-up Air Compressor. Can you say what the compressed air is used for?

But I think you have your answer based on the size of the original Startup Air Compressor. It's presumed the rotary screw compressors used to replace the original reciprocating compressors are rated for the same pressure (125 psi) and supply volume (30-40 CFM) and other than the maintenance headache (I presume it's maintenance issues that are causing the headaches...) they've been providing adequate air flow for whatever the compressed air is used for.

Thanks for any information you can provide. I'm just curious about this Startup Air Compressor and what the compressed air is required for. A 7.5 HP compressor would most likely be a 3-phase compressor and 30-40 CFM is not a small amount of air flow at 125 psi. Hmmmm.